The present application is based on Japanese Patent Application No. 2001-300346, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a fuel cutoff valve mounted on an upper part of a fuel tank and enabled to switch communication and cutoff between the fuel tank and the outside by opening and closing a connection conduit, which connects the inside of the fuel tank to the outside.
2. Related Art
Hitherto, there has been known such a kind of a fuel cutoff valve disclosed in JP-A-2000-266208 (corresponding to U.S. Pat. No. 6,286,539). FIG. 6 is a sectional view showing a conventional fuel cutoff valve. The fuel cutoff valve 110 is mounted on an upper part of a fuel tank FT and operative to switch communication and cutoff between the fuel tank FT and the outside by opening and closing a connection conduit 122, which connects the inside of the fuel tank to the outside. The fuel cutoff valve 110 comprises a casing 120, a float 130, and a cover 140. The cover 140 can be thermally welded to the upper part of the fuel tank FT and is made of a resin material having a higher fuel swelling property than the material of the casing 120. An engagement projection 126 formed on the casing 120 is engaged with an engagement hole 142 formed in the cover 140 as means for attaching the cover 140 to the casing 120. Moreover, a holding part 124 is formed in the casing 120. A fitting part 144 of the cover 140 is held by this holding part 144. In the valve of this configuration, when the fitting part 144 of the cover 140 is expanded owing to fuel swelling, the fitting part 144 is held by the holding part 124. At that time, when the cover 140 swells, the holding part 124 enhances a supporting force by increasing mechanical bond strength between the holding part 124 and the fitting part 144. Thus, such a holding part 124 provides stable opening/closing characteristics to the fuel cutoff valve 110.
However, the conventional fuel cutoff valve 110 has problems in that the structure of a mold for injection-molding of the holding part 124 and the fitting part 144 becomes complex and needs high dimensional accuracy.
The invention solves the problems of the conventional valve. Accordingly, an object of the invention is to provide a fuel cutoff valve, which does not have shakiness owing to fuel swelling and can obtain a stable valve-closing characteristic.
To solve the problems, according to the invention, there is provided a fuel cutoff valve adapted to be mounted on an upper part of a fuel tank for switching communication and cutoff between an inside and an outside of the fuel tank by opening and closing a connection conduit, the fuel cut off valve comprising:
a casing forming a valve chamber communicating with the fuel tank;
a cover including a cover welding end that is made of a first resin material, which is thermally weldable to the upper part of the fuel tank, and that is configured to be thermally welded to the upper part of the fuel tank, and a cover supporting part for supporting an upper part of the casing;
a valve element accommodated in the valve chamber to open and close the connection conduit;
a sealing member disposed on an outer periphery of the casing;
a seal holding member that is made of a second resin material, which is thermally weldable to the cover supporting part, and that has a higher shape stability against fuel than the cover,
the seal holding member including a pressing face adapted to press the sealing member from an outside of the casing and a holding-member-side welding end configured to be thermally welded to the cover supporting part so as to press the sealing member, thereby sealing the inside of the fuel tank from the outside and supporting the casing.
The casing of the fuel cutoff valve according to the invention has a valve chamber communicating with the fuel tank. A valve element accommodated in this valve chamber rises and falls by increasing and decreasing a buoyant force according to the level of fuel contained in the fuel tank. Thus, the valves opens and closes the connection conduit to thereby prevent the fuel from flowing out of the fuel tank. Further, the cover is made of a resin material, which can be thermally welded to the upper part of the fuel tank, and thermally welded thereto, so that the fuel cutoff valve is mounted on the upper part of the fuel tank. Consequently, the fuel cutoff valve can easily be mounted on the upper part of the fuel tank without needing joining members.
The casing is made of a resin material that has a lower fuel swelling property than the cover. Thus, a seat face for opening and closing a fuel path can be formed with high accuracy. Further, the seal holding member thermally welded to the cover supporting part has a high degree of the shape stability against the fuel. Thus, even when exposed to the fuel, the seal holding member does not largely swell. Instead, the seal holding member reliably holds the sealing member by the pressing face so that high sealing ability is maintained. Incidentally, shape stability is defined as a combined property of the stiffness and the fuel swelling property of the member in a fuel atmosphere, indicating sealing and holding property to the casing.
Furthermore, the seal holding member is thermally welded to the cover supporting part. Thus, the sealing ability of the part provided therebetween is enhanced. Moreover, the supporting force for the casing can be increased. Therefore, the fuel cutoff valve does not cause troubles due to the shakiness. That is, the fuel cutoff valve can obtain stable opening/closing characteristics without causing reduction in impact resistance (i.e. mechanical strength against an impact) and variation in level of fuel when the fuel cutoff valve opens and closes.
The adding of a fibrous material thereinto, the use of a resin material that excels in fuel swelling resistance over the cover, and the embedding of an insert member can be taken as measures to increase the shape stability still more.
Further, the following resin materials are used for thermally welding the cover to the fuel tank, and for welding the seal holding member to the cover. That is, the casing is made of a material selected from a group consisting of polyacetal, polyamide, polyphenylene sulfide, and polybutylene terephthalate or of a blend of these materials of the group. The cover is made of polyethylene. The seal holding member is made of polyethylene, into which fibrous materials are added. Incidentally, the fibrous materials are glass fibers and asbestos fibers to be added thereto so as to improve the mechanical and dimensional stability against the fuel swelling without impairing the properties of the resin materials.
Further, as another preferred embodiment of the cover, the cover may be configured so as to have a cover inner layer, which is formed in such a manner as to face the connection conduit and to support the cover supporting part, and a cover outer layer that is formed by two-color molding and chemically bonded to this cover inner layer and has the cover welding end. In this case, the cover inner layer and the cover outer layer may be adapted so that the cover inner layer and the cover outer layer are made of different resin materials that are thermally welded to each other, that the cover inner layer is made of a resin material, which can be thermally welded to the seal holding member, and that the cover outer layer is made of a resin material, which can be thermally welded to the upper wall of the fuel tank. For example, the fuel cutoff valve may be adapted so that the casing is made of a material selected from the group consisting of polyacetal, polyamide, polyphenylene sulfide, and polybutylene terephthalate or of a blend of these materials of the group, that the cover outer layer is made of polyethylene, and that the cover inner layer is made of modified polyamide, which can be thermally welded to polyethylene, and that the seal holding member is made of polyamide. Incidentally, the chemical adhesion property between the modified polyamide and polyethylene can be added to the modified polyamide by adding a polar functional group of, for example, a maleic acid to the modified polyamide.
Further, the seal holding member can be formed by using an insert member, which is embedded so as to surround the sealing member, so that the seal holding member has a higher shape stability than the cover. The insert member can be embedded by embedding a metallic member or a resin material that differs from the rein material of the seal holding member.
Additionally, the seal holding member may be constituted so as to have a case cover that covers a side wall and a lower opening of the casing and that is integrally formed.
Further, the seal member has a ring-like shape and performs a sealing by compressed with the seal holding member in a radially inner direction thereof, which is perpendicular to a direction of thermally welding the casing to the cover.